The present invention concerns a procedure for treating cellulose derivative fibres. More specifically, the invention concerns a procedure for regulating the properties of cellulose carbamate fibres. Furthermore, the invention concerns a novel procedure for manufacturing regenerated cellulose fibres.
In the Finnish patent application No. 61,033 and U.S. Pat. No. 4,404,369 is disclosed a procedure for manufacturing an alkali-soluble cellulose derivative from cellulose and urea at elevated temperature. The procedure is based on the fact that on heating urea to its melting point or to a higher temperature it begins to decompose into isocyanic acid and ammonia. Isocyanic acid in itself is not a particularly stable compound; it tends to trimerize into isocyanuric acid. Furthermore, isocyanic acid also tends to react with urea, whereby biuret is formed. Isocyanic acid also reacts with cellulose, producing an alkali-soluble cellulose derivative which is called cellulose carbamate. The reaction may be written as follows: ##STR1## The cellulose compound thus produced, cellulose carbamate, may be dried subsequent to washing and stored even over prolonged periods, or it may be dissolved in an aqueous alkali solution for manufacturing fibres, for instance. From this solution can be manufactured cellulose carbamate fibres or films by spinning or by extruding, in like manner as in the viscose manufacturing process. The keeping quality of cellulose carbamate and its transportability in dry state afford a great advantage compared with cellulose xanthate in the viscose process, which cannot be stored nor transported, not even in solution form.
If, for instance, continuous fibre or filament manufactured from cellulose carbamate appropriate for textile uses is desired, the carbamate is first dissolved in alkali, e.g. in aqueous sodium hydroxide solution. From this solution may then be precipitated fibre or film, for instance in like manner as in the manufacturing of viscose fibre cellulose is regenerated from the NaOH solution of cellulose xanthate. In this connection, the cellulose carbamate solution is spun through spinnerets into an acid precipitation bath, which causes precipitation of the cellulose carbamate. The precipitation may also be accomplished into lower alcohols such as methanol, ethanol or butanol, or into hot aqueous salt solutions.